INTRODUCTORY AND GENERAL REMARKS.
Function of an Electricity Meter-Classifications of Meters-Importance of Meters-Some Requisites of a Meter-Accuracy-Error Limits-Board of Trade Error Limits--Error Limits of the Physikalisch-Technische Reichsanstalt, Germany - Permanency of Calibration-Guarantee-Series and Shunt Losses-Criterions of a Meter-Selection of a Meter-Capacity of a Meter-Meters approved by the Board of Trade.
Function of an Electricity Meter. When a commodity is supplied to consumers for illuminating, heating, power, or other domestic purposes, it is necessary to accurately determine the amount of the commodity so used, and for this purpose measuring instruments, called meters, are installed on the consumers' premises. In the case of an electricity supply the commodity is electrical energy, and the meter is then termed an electricity meter, the function of which is to register the electrical energy which is used in a given time in any circuit in which flows a current of electricity. The meter does not necessarily measure electrical energy direct; it measures either this electrical magnitude or electrical quantity.
In either case, however, it registers in terms of the supply unit of electrical energy. In other words, the difference between two readings of the scale, dials, or counter of the registering part of the meter gives, within certain error limits, the amount of the electrical energy consumed in a given period in terms of the supply unit, generally without the use of a multiplier, the two readings being taken at the commencement and termination of the period under consideration. The supply unit in this country is the Board of Trade (B.O.T.) unit, one B.O.T. unit being equal to one kilowatt-hour, or 1000 watthours. In France the hectowatt-hour is largely used (one hectowatt-hour equals 100 watt-hours), and in Germany and America the unit is the kilowatt-hour. Classifications of Meters. According to the electrical magnitude to be measured, the instrument is termed an energy meter or a quantity meter. An energy meter is more usually spoken of as a watt-hour, and a quantity meter as an ampere-hour meter.
As the unit of electrical energy in this country with reference to meter registrations is the kilowatt-hour, the term 'kilowatt-hour meter' is preferable to the one watt-hour meter,' commonly used.
The operation of an electricity meter depends on one or other of the well